It was among two helicopters that were conducting aerial frost control on a local field.

The cause of the crash is under investigation

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

Search crews have located the wreckage of a helicopter that disappeared in central California while trying to keep crops from freezing, and they say the female pilot is dead, Kern County Sheriff's Department officials said Wednesday.

The crash site was found at 9:50 a.m., about four hours after the helicopter vanished early on Wednesday morning, Sheriff's spokesman Ray Pruitt said.

A sheriff's air unit spotted the wreckage in a vineyard southeast of Delano with the help of the pilot of another helicopter who had seen the aircraft go down, Pruitt said.

The returning pilot had tried unsuccessfully to contact the missing pilot by radio. Officials said heavy fog was present in the area at the time of the crash, limiting visibility. The fog made the search difficult as well.

Authorities have not released the victim's name, but said she was in her 60's.

Federal Aviation Administration spokesman Ian Gregor has said the helicopter was returning to Delano Airport in Kern County when it disappeared. It was among two helicopters that were conducting aerial frost control on a local field.

Officials with San Joaquin Helicopter, a Delano-based company, confirmed the helicopter was part of their fleet. During cold spells, helicopters move warmer air down onto threatened crops.

The National Transportation Safety Board and the Federal Aviation Administration are investigating the causes of the crash.